Some aspects of plasma polymerization investigated by pulsed R.F. discharge

The polymerization of organic compounds in glow discharge (plasma polymerization) was investigated by using pulsed R.F. discharge (100 μsec on, 900 μsec off). The effects of pulsed discharge on polymer deposition rate, pressure change in plasma, ESR signals of free spins in both plasma polymer and substrate, and the contact angle of water on the plasma polymer surface were investigated for various organic compounds. The results are correlated to the mechanisms of polymer formation in plasma (plasma polymerization) which has been postulated as repeating processes of stepwise (propagation) reactions. The effect of the pulse is different from one group of organic compounds to another depending on whether or not they contain an olefinic double bond and/or a triple bond. The main difference seems to be the addition polymerization which can occur exclusively during the off-period of pulsed discharge. Ultraviolet emission from pulsed discharge is much less than from continuous discharge. Consequently, the fragmentation of the monomer and the free-radical formation in the substrate are less with the pulsed discharge. Properties of polymers from some organic compounds formed in continuous and in pulsed discharge were found to be significantly different, and the differences were postulated from the changes of polymerization mechanisms in the pulsed discharge.     

Permeation properties to hydrocarbons,perfluorocarbons and chlorofluorocarbons of cross-linked membranes of polymethacrylates with poly(ethylene oxide) and perfluorononyl moieties

Two kinds of cross-linked polymer membranes were prepared by photo polymerization. One of them (PEO membrane) is a co-polymer of methoxy-terminated poly(ethylene glycol) methacrylate (MEMA) and poly(ethylene glycol) dimethacrylate (EDMA) in feed ratio of 70/30 in wt%. The other (PF/PEO membrane) is a co-polymer of 1H,1H,9H-hexadecafluorononyl methacrylate and EDMA in feed ratio of 70/30 in wt%. The block lengths of poly(ethylene oxide) (PEO) are 9 and 14 for MEMA and EDMA, respectively. Permeation properties of inorganic gases, hydrocarbons, perfluorocarbons and chlorofluorocarbons (CFCs) were investigated for these membranes compared with a silicone rubber (SR) membrane. The PF/PEO membrane is inferior to the SR membrane as for CFCs/N₂ separation because the former has lower permeabilities. The PEO membrane has good performance for separation of hydrocarbons and CFCs from N₂ or perfluorocarbons.     

Plasma polymerization investigated by the substrate temperature dependence

Plasma polymerization of tetra fluoroethylene (TFE), perfluoro-2-butyl-tetrahydrofuran (PFBTHF), ethylene, and styrene were investigated in various combinations of monomer flow rates and discharge wattages for the substrate temperature range of ?50 to 80°C. The polymer deposition rates can be generally expressed by k₀ = Ae^?bt, where k₀ is the specific deposition rate given by k₀ = (deposition rate)/(mass flow rate of monomer), A is the preexponential factor representing the extrapolated value of k₀ at zero absolute temperature, and b is the temperature-dependence coefficient. It was found that the value of b is not dependent on the condensibility of monomer but depends largely on the group of monomer; that is, perfluorocarbons versus hydrocarbons. The values of A are dependent on domains of plasma polymerization. In the energy deficient region A is given by A = α(W/FM)ⁿ, where α is the proportionality constant, W is discharge wattage, FM is the mass flow rate, and n is close to unity. In the monomer deficient region A becomes a constant. The kinetic equation is discussed in view of the bicyclic rapid step-growth polymerization mechanisms.     

Behavior and surface energies of polybenzoxazines formed by polymerization with argon,oxygen, and hydrogen plasmas

Polybenzoxazine (PBZZ) thin films can be fabricated by the plasma‐polymerization technique with, as the energy source, plasmas of argon, oxygen, or hydrogen atoms and ions. When benzoxazine (BZZ) films are polymerized through the use of high‐energy argon atoms, electronegative oxygen atoms, or excited hydrogen atoms, the PBZZ films that form possess different properties and morphologies in their surfaces. High‐energy argon atoms provide a thermodynamic factor to initiate the ring‐opening polymerization of BZZ and result in the polymer surface having a grid‐like structure. The ring‐opening polymerization of the BZZ film that is initiated by cationic species such as oxygen atoms in plasma, is propagated around nodule structures to form the PBZZ. The excited hydrogen atom plasma initiates both polymerization and decomposition reactions simultaneously in the BZZ film and results in the formation of a porous structure on the PBZZ surface. We evaluated the surface energies of the PBZZ films polymerized by the action of these three plasmas by measuring the contact angles of diiodomethane and water droplets. The surface roughness of the films range from 0.5 to 26 nm, depending on the type of carrier gas and the plasma‐polymerization time. By estimating changes in thickness, we found that the PBZZ film synthesized by the oxygen plasma‐polymerization process undergoes the slowest rate of etching in CF₄ plasma. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 4063–4074, 2004     

Perfluorinated and partially fluorinated organic compounds. Preparation,characterization and application

Electrochemical fluorination (ECF) of various heterocyclic compounds has been investigated. α,ω-Dimorpholinoalkanes of different chain length (n = 1-6) and of morpholinocyclohexene gave the perfluoro derivatives in yields up to 45%. The crystal and molecular structures of the perfluorinated compounds are presented. The mechanism of ECF for these compounds is discussed on the basis of a steric model. Perfluorocarbon emulsions of second generation were prepared by means of F-dimorpholines and F-cyclohexylmorpholine, acting both as oxygen carriers and as interfacial active compounds (IFACs). The stabilizing effect of these IFACs is interpreted. Semifluorinated alkanes, R_fR_h, are chemically inert and non-toxic. They are useful for blood substitutes in two ways: as co-surfactants to stabilize emulsions with perfluorocarbons and as oxygen carriers instead of perfluorocarbons. The high density of perfluorocarbons cause problems in some field of application in medicine. Therefore symmetrical diethers of the type R_F(CH₂)_mO(CH₂)_nO(CH₂)_mR_F were synthesized. These are inert and biocompatible compounds. Diethers with long R_F-tail and long hydrocarbon spacer are ideal solubilizers for perfluorocarbons with hydrocarbons and vice versa. The diethers with short hydrocarbon spacer and long R_F-tail can be applied in biological systems, because they are not soluble in lipid tissues. Perfluorocarbons (e. g. F-decalin, F-octane) are used as medical tools in ophthalmology, their purity is essential. Not totally fluorinated compounds (1 H-perfluoroalkanes, α,ω-dihydrogenoperfluoroalkanes) are characterized and discussed. 1H-perfluoroalkane is also formed by nucleophilic attack on perfluoroalkyl halide.     

Diverse effects of β-carotene on secretion and expression of VEGF in human hepatocarcinoma and prostate tumor cells

Oral administration of β-carotene (BC) was found to exert opposite effects on plasma levels of vascular endothelial growth factor (VEGF) in two animal models. One study in nude mice injected via tail vein with hepatocarcinoma SK-Hep-1 cells showed that BC decreases the plasma VEGF level, whereas the other study in nude mice injected subcutaneously with prostate tumor PC-3 cells showed that BC increases the plasma VEGF level. Herein we investigated whether BC (0.5-20 μM) possesses diverse effects on VEGF secretion in SK-Hep-1, PC-3 and melanoma B16F10 cells. We found that incubation of SK-Hep-1 cells with BC (1-20 μM) for 6 h significantly decreased VEGF secretion, whereas BC (1-10 μM) significantly increased the VEGF secretion in PC-3 cells. However, these effects disappeared at 12 h of incubation. Similar effects occurred in VEGF mRNA and protein expression after treatment of SK-Hep-1 and PC-3 cells with BC for 6 h. In contrast, BC (0.5-20 μM) did not affect mRNA and protein expression and secretion of VEGF in B16F10 cells. We also found that the proliferation of SK-Hep-1 and B16F10 cells was significantly inhibited by 20 μM BC at 6 and 12 h of incubation, whereas the proliferation of PC-3 cells was significantly inhibited by 20 μM BC at 12 h of incubation. In summary, the present study demonstrated the tumor-specific effect of BC on VEGF secretion in different cancer cell lines.     

The Role of Halogens in the Plasma Polymerization of Hydrocarbons

Vinyl chloride, vinyl fluoride, and tetrafluoroethylene were polymerized in a radio frequency electric glow discharge. It was found that when compared with the unhalogenated simple hydrocarbons, the rates of polymer deposition are in the order vinyl chloride, acetylene, tetrafluoroethylene, vinyl fluoride, ethylene. This observation can be rationalized by considering the ease with which free radical and unsaturated species can be formed in the plasma. IR spectra show that the structures of plasma-polymerized vinyl chloride and vinyl fluoride are in many respects similar to the plasma-polymerized hydrocarbon. The spectrum of plasma-polymerized tetrafluoroethylene, however, does not resemble that of conventional polytetrafluoroethylene. Addition of dichlorodifluoromethane to the monomer stream dramatically increased the polymer deposition rate; the effect is more subdued for chloromethane and is negligible for tetrafluoromethane. Elemental analysis indicates that little of the added halogens is present in the resultant polymers. Thus the halogenated compounds appear to act as a gas phase catalyst for the plasma polymerization of hydrocarbons.     

Perfluorocarbon-hydrocarbons self-assembly: halogen bonding mediated intermolecular recognition

Halogen bonding is discussed as an interaction that is capable of overcoming the reluctance shown by fluorinated compounds towards interactions with hydrocarbons. This non-covalent interaction is sufficiently strong to enact formation of supramolecular architectures where perfluorocarbons, hydrocarbons, and inorganic salts are self-assembled. Examples are discussed which exemplify the consistency and versatility of this interaction in affording numerous and structurally different hybrid materials. The importance of fluorine in determining the overall packing of the formed architectures is also highlighted.     

Polymerisation de l'acide methacrylique en masse et en solution

In spite of the fact that the bulk polymerization of methacrylic acid proceeds under precipitating conditions, all conversion curves are linear and start from the origin. The overall activation energy of the gamma ray initiated reaction is very small: 1.3 kcal/mol. Methanol and water are solvents for the polymer but also form monomer-solvent complexes through H-bonds. It was found that, over a limited concentration range in these solvents, the reaction becomes auto-accelerating both in precipitating and homogeneous reaction media. Non-polar solvents (hydrocarbons) lead to a significant reduction in the polymerization rate but this effect is not as pronounced as for acrylic acid. Chlorinated derivatives reduce the polymerization rate of acrylic acid to the same extent as hydrocarbons but, for methacrylic acid, chlorinated derivatives lead to sensitization. By analogy with earlier results for acrylic acid, it is assumed that the auto-acceleration observed in water and methanol solutions is caused by a “matrix effect”. In bulk, the monomer undoubtly also associates with the polymer but, in view of the bulky methyl groups, the regularly oriented structure which favours propagation presumably never arises. The very small activation energy of the polymerization suggests that chain termination requires a significant activation energy. The mechanism of this process is not clear.     

Simultaneous determination of trace amounts of sulphur hexafluoride and cyclic perfluorocarbons in reservoir samples by gas chromatography

Summary Both sulphur hexafluoride and a group of compounds among the perfluorinated cyclic hydrocarbons: perfluorodimethyl cyclobutane, perfluoromethyl cyclopentane, perfluoromethyl cyclohexane and the 1,2- and 1,3-isomers of perfluordimethyl cyclohexane are well known to be good gas tracers, in various applications. Unfortunately different methods have been used for the analysis of SF₆ and the perfluorocarbons. Therefore, in many cases, the analytical costs may have hindered the use of both SF₆ and the perfluorocarbons in the same tracer experiments. The analytical method described in this paper enables the determination of both types of gas tracer in one single run. The new method has already replaced two former methods and was used to run the gas tracer analysis routinely, proving the reliability of the method.     

In situ doping polymerization of polyaniline microtubules in the presence of β‐naphthalenesulfonic acid

Conducting microtubules of Polyaniline (PANI) were synthesized for the first time by the “in situ doping polymerization” method in the presence of β‐naphthal‐ enesulfonic acid (NSA) as dopant. Different doping methods, such as “immerse doping” and “grind doping,” and different synthetic conditions, such as molar ratio of aniline (An) to NSA (An/NSA), concentration of NSA in the polymerization media, reaction temperature, and time were investigated to understand the formation of microtubules. It was found that the PANI–NSA microtubules can be formed only by the “in situ doping polymerization” method, and the above synthetic conditions strongly affect the formation of the PANI–NSA microtubules, especially the molar ratio of An to NSA. An optimal condition was found under which tubules with 1–3 μm in diameter and 10–50 μm in length were obtained. The morphology of PANI–NSA tubules was proved by SEM and TEM, and their backbone structure was characterized by FTIR, UV‐VIS, XPS, and X‐ray diffraction. Results of these measurements showed that the molecular structures of the resulted PANI–NSA microtubules were identical to that of PANI–HCl synthesized by conventional method. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 151–157, 1999     

Conversion of natural gas to C2 hydrocarbons via cold plasma technology

The plasma technology served as a tool in unconventional catalysis has been used in natural gas conversion, because the traditional catalytic methane oxidative coupling reaction must be performed at high temperature on account of the stability of methane molecule. The focus of this research is to develop a process of converting methane to C2 hydrocarbons with non-equilibrium plasma technology at room temperature and atmospheric pressure. It was found that methane conversion increased and the selectivity of C2 hydrocarbons decreased with the voltage. The optimum input voltage range was 40-80 V corresponding to high yield of C2 hydrocarbons. Methane conversion decreased and the selectivity of C2 hydrocarbons increased with the inlet flow rate of methane. The proper methane flow rate was 20-40 ml/min (corresponding residence time 10-20 s). The experimental results show that methane conversion was 47% and the selectivity of C2 hydrocarbons was 40% under the proper condition using atmospheric DBD cold plasma technology. It was found that the breakdown voltage of methane VB was determined by the type of electrode and the discharge gap width in this glow discharge reactor. The breakdown voltage of methane VB,min derived from the Paschen law equation was established.     

Effects of Cathode and Anode on Deposition of Trimethylsilane in Glow Discharge

DC cathodic polymerization of trimethylsilane (TMS) was carried out in plasma reactors with and without using anode assembly. In DC cathodic polymerization, the TMS plasma polymers are mainly deposited on the cathode (substrate) surface. As a result, fast deposition of TMS plasma polymers was easily achieved in DC cathodic polymerization as compared with AF or RF plasma polymerization. DC cathodic polymerization without using anode assembly has its advantageous features that the size and number of substrates (as cathodes) are not restricted by the size and the location of anode assembly. It was found that the maximum deposition rate on the cathode surfaces was obtained without anode assembly. The DC cathodic polymerization of TMS was conducted also in a large volume reactor with multiple cathodes (substrates). The same deposition mechanisms for DC cathodic polymerization with a single cathode also apply to the multiple cathodes. Uniform deposition on each cathode could be obtained with appropriate spacing of multiple cathodes and by adjusting the operational parameters, which are based on the current density and the system pressure.     

Synthesis and ring‐opening polymerization of macrocyclic aryl ketone oligomers

A series of macrocyclic aryl ketone oligomers were prepared by the reaction of phthaloyl dichloride or isophthaloyl dichloride with various bridge‐linking electron‐rich aromatic hydrocarbons 3a–d under pseudo‐high dilution conditions in the presence of Lewis base via Friedel–Crafts acylation reaction. Detailed structural characterization of these oligomers confirmed the cyclic nature by a combination of MALDI‐TOF‐MS, GPC, and ¹H NMR analyses. These cyclic ketone oligomers have high solubility in organic solvents and the cyclic oligomers derived from phthaloyl dichloride are amorphous. The cyclic ketone oligomers readily undergo anionic ring‐opening polymerization in the melt by using potassium 4,4′‐biphenoxide as the initiator, producing linear, high molecular weight poly(ether ketone)s. Moreover, the isothermal chemorheology of the ring‐opening polymerization of cyclic oligomers 4a and 4b was also investigated. The results show that the shear viscosity of the molten reactive mixture is lower than 10 Pa · S at a constant shear rate of 0.05 rad/sec and increases slowly in the initial stage of ring‐opening polymerization. Copyright © 2009 John Wiley & Sons, Ltd.     

Conversion of natural gas to C_2 hydrocarbons via cold plasma technology

The plasma technology served as a tool in unconventional catalysis has been used in natural gas conversion,because the traditional catalytic methane oxidative coupling reaction must be performed at high temperature on account of the stability of methane molecule.The focus of this research is to develop a process of converting methane to C2 hydrocarbons with non-equilibrium plasma technology at room temperature and atmospheric pressure.It was found that methane conversion increased and the selectivity of C2 hydrocarbons decreased with the voltage.The optimum input voltage range was 40-80 V corresponding to high yield of C2 hydrocarbons.Methane conversion decreased and the selectivity of C2 hydrocarbons increased with the inlet flow rate of methane.The proper methane flow rate was 20-40 ml/min (corresponding residence time 10-20 s).The experimental results show that methane conversion was 47% and the selectivity of C2 hydrocarbons was 40% under the proper condition using atmospheric DBD cold plasma technology.It was found that the breakdown voltage of methane VB was determined by the type of electrode and the discharge gap width in this glow discharge reactor.The breakdown voltage of methane VB,min derived from the Paschen law equation was established.     

二甲基苯胺等离子体聚合及聚合物结构与性能的研究

应用外部电容耦合式等离子体聚合装置，研究了二甲基苯胺等离子体聚合规律，找到了最佳的聚合条件。通过热失重，红外光谱、Ｘ－射线衍射、电子衍射和接触角测定等，研究聚合物结构与性能。电导率测定表明二甲基苯胺等离子体聚合物具有半导体性质。     

Element selective detection of chlorine in capillary gas chromatography by wavelength modulation diode laser atomic absorption spectrometry in a microwave induced plasma

A new element selective detector for gas chromatography is presented. The detector, based on wavelength modulation diode laser atomic absorption spectrometry in a microwave induced helium plasma, is used for measurements of chlorinated hydrocarbons by absorption of excited, metastable chlorine atoms. Indications of complete dissociation of the halocarbons in the plasma have been found. Preliminary detection limits of the order of 1 μg ml⁻¹ or 80 pg s⁻¹ have been found for different halocarbons.     

笼形树脂的合成及结构—性能关系的研究

在过氧化苯甲酰(BPO)存在下,甲基丙烯酸(MAA)与二乙烯基苯(DVB)在水溶液中与聚丙烯(PP)进行非均相接枝共聚,接枝物经二甲苯除去未接枝或非交联低接枝的聚丙烯,得笼形聚羧酸树脂。在非均相接枝体系中加入10％烷烃或芳烃(石油醚、甲苯)、卤代烃(三氯乙烷、氯苯)等非水溶性化合物或二甲基甲酰胺等水溶性化含物,单体和引发剂在三相体系中将重新分配,对单体转化率和最终产物—笼形树脂的组成和反应性能都有显著的影响。笼形树脂的羧基相对含量是决定树脂的结构和反应性能的主要因素。在相同的交联密度(X=6.25mol％)条件下,笼形树脂在水相中的溶胀度与树脂的羧基相对含量成正比。溶胀度与交联密度关系不服从Boyd-Soldano经验方程,归因于笼形树脂空心结构所赋有的双向溶胀特性。笼形树脂与VO~(2+)离子的交换速度随树脂的羧基相对含量的增大而相应提高,交换动力学表明,树脂的传质效应是交换速度的主要因素,但它被笼形树脂的特殊结构所削弱。以不同的反应介质合成的笼形树脂负载VO~(2+)离子(PV)与硫脲(TU)组合作引发体系,在硝酸溶液中引发丙烯腈聚合,聚合速度同是2.35×10~(-4)mol·L~(-1)·S~(-1),只有一例除外。表明了聚合速度取决于树脂的载VO~(2+)量,它和合成条件及方式有关。     

Preparation and thermodynamic stability of micron-sized, monodisperse composite polymer particles of disc-like shapes by seeded dispersion polymerization

Micron-sized, monodisperse composite polymer particles having "disc-like" and "polyhedral" shapes were prepared by seeded dispersion polymerization of 2-ethylhexylmethacrylate (EHMA) with 2.67-mum-sized polystyrene (PS) seed particles in methanol/water media in the presence of droplets of various saturated hydrocarbons and evaporation of the hydrocarbon after the polymerization. Such nonspherical shapes were based on the volume reduction due to the evaporation. The primary factors influencing the particle shape seemed to be the absorption rate of the hydrocarbon into the resulting PS/poly(EHMA)/hydrocarbon composite particles during the polymerization, which affected the viscosities and the volumes of the PS and poly(EHMA) phases. It was found that the morphological development during the polymerization was retarded at "hamburger-like" morphology, which is a precursor of the disc-like particle, although this morphology is a thermodynamically metastable state.     

Plasma polymerization of aniline on different surface functionalized substrates

The plasma polymerization of aniline on different surface functionlized low-density polyethylene (LDPE) substrates was investigated, and the resulting polymer was characterized by X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, scanning electron microscopy, and atomic force microscopy. The results showed that the structure of plasma-polymerized polyaniline was rather different from polyaniline synthesized by conventional chemical and electrochemical methods. This difference may be due to extensive coupling reactions and cross-linking reactions during the plasma polymerization process. The use of acrylic acid graft copolymerized LDPE substrate significantly enhanced the adhesion of the polyaniline to the substrate over that observed with pristine LDPE. The plasma polymerized polyaniline can be rendered electrically conductive if the polymerization is carried out on a polystyrenesulfonic acid-coated LDPE substrate. Conductivity can also be induced by acid protonation of the polyaniline by HClO(4). The reaction of the plasma-polymerized polyaniline with viologen grafted on the substrate under UV irradiation and with AuCl(3) and Pd(NO(3))(2) in acid solutions was also investigated.